Organic light emitting diode display

ABSTRACT

An OLED display includes a substrate, a first electrode on the substrate, an organic emission layer on the first electrode, a second electrode on the organic emission layer, an insulating layer substantially covering the second electrode and having an opening that exposes a center portion of the second electrode, and a power supply electrically coupled with the second electrode through the opening of the insulating layer and configured to supply power to the second electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2010-0138193 filed in the Korean IntellectualProperty Office on Dec. 29, 2010, the entire contents of which areincorporated herein by reference.

BACKGROUND

1. Field

An exemplary embodiment of the present invention relates to an organiclight emitting diode (OLED) display.

2. Description of Related Art

An organic light emitting diode (OLED) display is a self emissivedisplay device that displays images with organic light emitting diodes.The organic light emitting diode emits light with current receivedthrough a power wire. In general, the power wire is coupled to an edgeof a substrate of the OLED display and transmits a current to theorganic light emitting diode.

However, the power wire has resistance, and a voltage drop (IR-drop)occurs due to the resistance. Thus, luminance of light emitted from theOLED display may be non-uniform at an edge and a center of thesubstrate.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the describedtechnology, and therefore it may contain information that does not formthe prior art that is already known in this country to a person ofordinary skill in the art.

SUMMARY

The described technology has been made in an effort to provide anorganic light emitting diode (OLED) display of which uniformity ofluminance is improved and having a simple structure.

An OLED display according to an exemplary embodiment includes asubstrate, a first electrode on the substrate, an organic emission layeron the first electrode, a second electrode on the organic emissionlayer, an insulating layer substantially covering the second electrodeand having an opening that exposes a center portion of the secondelectrode, and a power supply electrically coupled with the secondelectrode through the opening of the insulating layer and configured tosupply power to the second electrode.

The power supply may include a flexible printed circuit contacting thecenter portion of the second electrode through the opening of theinsulating layer.

The power supply may include a connection metal layer on the insulatinglayer and contacting the center portion of the second electrode throughthe opening of the insulating layer, and a flexible printed circuitcontacting the connection metal layer at an edge of the substrate.

The first electrode may include a transparent or transflective material,and the second electrode may include a reflective material.

Thicknesses of areas of the second electrode at a center of thesubstrate and at an edge of the substrate may be larger than a thicknessof remaining areas of the second electrode.

Further, an OLED display according to another exemplary embodimentincludes a substrate, a first electrode on the substrate, an organicemission layer on the first electrode, and a second electrode on theorganic emission layer, wherein a thickness of an area of the secondelectrode at a center of the substrate is larger than a thickness of anarea of the second electrode at an edge of the substrate.

The OLED display may further include a power supply electrically coupledwith the second electrode at the edge of the substrate and configured tosupply power to the second electrode.

The power supply may include a flexible printed circuit.

The OLED display may further include an insulating layer substantiallycovering the second electrode and having an opening exposing a centerportion of the second electrode, and a power supply electrically coupledwith the second electrode through the opening of the insulating layerand configured to supply power to the second electrode.

The power supply may include a flexible printed circuit contacting thecenter portion of the second electrode through the opening of theinsulating layer.

The power supply may include a connection metal layer on the insulatinglayer and contacting the center portion of the second electrode throughthe opening of the insulating layer and a flexible printed circuitcontacting the connection metal layer at the edge of the substrate.

The first electrode may include a transparent or transflective material,and the second electrode may include a reflective material.

According to the exemplary embodiments, luminance of the OLED displaycan be improved in uniformity while having a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top plan view of an OLED display according to afirst exemplary embodiment.

FIG. 2 is a schematic cross-sectional view of the OLED display of FIG. 1taken along the line II-II.

FIG. 3 is an enlarged cross-sectional view of the OLED display of FIG.1.

FIG. 4 is a schematic top plan view of an OLED display according to asecond exemplary embodiment.

FIG. 5 is a cross-sectional view of the OLED display of FIG. 4 takenalong the line V-V.

FIG. 6 is a cross-sectional view of an OLED display according to a thirdexemplary embodiment.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art will realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

Like reference numerals designate like elements throughout thespecification. In exemplary embodiments other than the first exemplaryembodiment among several exemplary embodiments, elements different fromthose of the first exemplary embodiment will be described.

Further, a size and thickness of each of the elements that are displayedin the drawings are described for better understanding and ease ofdescription, and the present invention is not limited by the describedsize and thickness.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. In the drawings, for better understandingand ease of description, thicknesses of some layers and areas areexcessively displayed, or exaggerated. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present.

Hereinafter, an organic light emitting diode (OLED) display according toa first exemplary embodiment will be described with reference to FIG. 1and FIG. 2.

As shown in FIG. 1 and FIG. 2, an OLED display 101 according to thefirst exemplary embodiment includes a substrate 111, a driving circuitDC, an organic light emitting element 70, and a power supply 901.

The substrate 111 may be formed with a transparent insulating substratemade of glass, quartz, ceramic, and the like, or may be formed with atransparent flexible substrate made of plastic.

As shown in FIG. 3, the driving circuit DC includes a thin filmtransistor 10, and the thin film transistor 10 is coupled with theorganic light emitting element 70. That is, the organic light emittingelement 70 emits light according to a driving signal transmitted fromthe driving circuit DC to display an image. In further detail, the thinfilm transistor 10 includes a semiconductor layer 133, a gate electrode153, a source electrode 135, and a drain electrode 137. The drainelectrode 137 is coupled with a first electrode 710 of the organic lightemitting element 70.

In FIG. 3, a semiconductor layer 133 of the thin film transistor 10 maybe a polycrystalline semiconductor layer 133, and has a top gatestructure in which a gate electrode 153 is formed on the semiconductorlayer 133. However, the first exemplary embodiment is not limitedthereto. Thus, the structure of the thin film transistor 10 may bevariously modified within a range known to a person skilled in the art.

The OLED display 101 further includes a buffer layer 120. The bufferlayer 120 may be formed through chemical vapor deposition or physicalvapor deposition, and may have a single-layered structure or amulti-layered structure including various insulating layers, such as asilicon oxide film, silicon nitride film, and the like, known to theskilled person in the art.

The buffer layer 120 serves to prevent moisture or impurities generatedfrom the substrate 111 from spreading or from infiltrating, to smooththe surface, and to regulate a heat transfer speed during acrystallization process performed for forming the semiconductor layer133 to thus accomplish desirable crystallization.

According to other embodiments of the present invention, the bufferlayer 120 may be omitted depending on the type and process conditions ofthe substrate 111.

The organic light emitting element 70 includes the first electrode 710,an organic emission layer 720, and a second electrode 730. The firstelectrode 710 is an anode that is a hole injection electrode, and thesecond electrode 730 is a cathode that is an electron injectionelectrode. However, the first exemplary embodiment is not limitedthereto. That is, the first electrode 710 may be a cathode and thesecond electrode 730 may be an anode.

The organic emission layer 720 has a multi-layered structure includingan emission layer and at least one of a hole injection layer (HIL), ahole transport layer (HTL), an electron transport layer (ETL), and anelectron injection layer (EIL). Excluding the emission layer 720, otherlayers may be omitted as necessary. If the organic emission layer 720includes all the layers, the hole injection layer (HIL) is disposed onthe transparent layer, which is the hole injection electrode, and thehole transport layer (HTL), the emission layer, the electron transportlayer (ETL), and the electron injection layer (EIL) are sequentiallystacked thereon. Alternatively, the organic emission layer 720 mayinclude other layers as necessary.

The first electrode 710 is formed for each pixel or pixel unit. Here,the pixel is the minimum unit for the OLED display 101 to display animage. Meanwhile, the second electrode 730 is formed throughout severalpixels, or formed throughout the front surface of the substrate 111.

In addition, the first electrode 710 is formed with a transparentmaterial or a transflective material, and the second electrode 730 isformed with a reflective material. The transparent material includes atleast one of indium tin oxide (ITO), indium zinc oxide (IZO), zincindium tin oxide (ZITO), gallium indium tin oxide (GITO), indium oxide(In₂O₃), zinc oxide (ZnO), gallium indium zinc oxide (GIZO), galliumzinc oxide (GZO), fluorine tin oxide (FTO), and aluminum-doped zincoxide (AZO).

The reflective material and the transflective material may be formedwith a metal. In this case, the reflective material and thetransflective material are determined by thickness. In general, thetransflective material may have a thickness of a range between 5 nm to100 nm, and the thickness of the reflective material may be relativelylarger than that of the transflective material. Depending on thethickness of the transflective material, transmittance and reflectivityof light are changed. In further detail, transmittance of the light isincreased as the thickness of the transflective material is decreased,and reflectivity of the light is decreased as the thickness of thetransflective material is increased. Further, transmittance of lightvaries according to thickness. When the thickness of the transflectivematerial is larger than 100 nm, transmittance of light is significantlydecreased. When the thickness of the transflective material is less than5 nm, an electric characteristic is deteriorated.

Further, when the first electrode 710 is formed with a transflectivematerial and the second electrode 730 is formed with a reflectivematerial, light use efficiency of the OLED display 101, that is,luminance of the OLED display 101, can be improved using a microcavityeffect. The microcavity effect can be maximized by controlling adistance between the first electrode 710 and the second electrode 730 ofthe organic light emitting element 70.

The OLED display 101 may further include a pixel defining layer 190. Thepixel defining layer 190 has an opening portion that at least partiallyexposes the first electrode 710. The organic emission layer 720 emitslight in the opening portion of the pixel defining layer 190. That is,the opening portion of the pixel defining layer 190 defines an areawhere light is substantially emitted.

Referring to FIG. 1 and FIG. 2, the OLED display 101 further includes aninsulating layer 800 covering the second electrode 730. The insulatinglayer 800 has an opening that partially exposes a center portion of thesecond electrode 730.

The power supply 901 is electrically coupled with the second electrode730 and supplies power thereto. The power supply 901 includes a flexibleprinted circuit (FPC) contacting the center portion of the secondelectrode 730 through the opening 807 of the insulating layer 800. Theflexible printed circuit (FPC) contacts the second electrode 730 throughan anisotropic conductive film (ACF) 851. The anisotropic conductivefilm 851 includes an adhesive layer and conductive balls included in theadhesive layer, and may further include various configurations known toa person skilled in the art.

With such a configuration, the OLED display 101 according to the firstexemplary embodiment can have improved uniformity while having asimplified structure. That is, the luminance in the center portion ofthe OLED display 101 can be prevented from being further deterioratedcompared to a peripheral area thereof.

Hereinafter, an OLED display 102 according to a second exemplaryembodiment will be described with reference to FIG. 4 and FIG. 5.

As shown in FIG. 4 and FIG. 5, the OLED display 102 according to thesecond exemplary embodiment includes a connection metal layer 601 formedon an insulating layer 800, and partially contacting a center portion ofa second electrode 730 through an opening 807 of the insulating layer800, and a power supply having a flexible printed circuit (FPC) 902contacting the connection metal layer 601 at an edge of a substrate 111.That is, the flexible printed circuit (FPC) 902 is attached to the edgeof the substrate 111, but supplies power through the center portion ofthe second electrode 730 through the connection metal layer 601.

With such a configuration, the OLED display 102 according to the secondexemplary embodiment can have improved uniformity while having asimplified structure.

Hereinafter, a third exemplary embodiment will be described withreference to FIG. 6.

As shown in FIG. 6, in an OLED display 103 according to the thirdexemplary embodiment, the thickness of a second electrode 735 of anorganic light emitting element 70 at an edge of a substrate 111 isrelatively smaller than the thickness at a center of the substrate 111.That is, resistance of the center portion of the second electrode 735 isreduced by increasing the thickness at the center portion thereof. Thus,a voltage drop (IR-drop) occurs due to the resistance of the secondelectrode 735 so that deterioration of luminance at the center portionof the OLED display 103 can be suppressed.

In FIG. 6, the flexible printed circuit (FPC) 902, that is, a powersupply, is coupled with the second electrode 735 at the edge of thesubstrate 111, but the third exemplary embodiment is not limitedthereto. Thus, as in the first and second exemplary embodiments, theflexible printed circuit (FPC) 902 partially electrically couples thecenter portion of the second electrode 735, and the thickness of thecenter portion of the second electrode 735 can be increased.

With such a configuration, the OLED display 103 according to the thirdexemplary embodiment can have improved uniformity while having asimplified structure.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, and their equivalents.

Description of Some of the Reference Characters 10 thin film transistor70 organic light emitting element 101, 102, 103 organic light emittingdiode (OLED) display 111 substrate main body 120 buffer layer 190 pixeldefining layer 601 connection metal layer 710 first electrode 720organic emission layer 730, 735 second electrode 800 insulating layer807 opening 901 power supply DC: driving circuit

What is claimed is:
 1. An organic light emitting diode (OLED) displaydevice comprising: a substrate; a plurality of first electrodes on thesubstrate; a plurality of organic emission layers on respective ones ofthe first electrodes; a second electrode as a common electrode commonlyon the plurality of organic emission layers for supplying power to allof the organic emission layers; an insulating layer substantiallycovering the second electrode and having a single opening for exposing acenter portion of the second electrode; and a power supply electricallycoupled with the second electrode through the opening of the insulatinglayer and configured to supply the power to all of the organic emissionlayers via the second electrode.
 2. The OLED display device of claim 1,wherein the second electrode is thicker at a center of the substratethan at an edge of the substrate.
 3. The OLED display device of claim 1,wherein the power supply comprises a flexible printed circuit contactingthe center portion of the second electrode through the opening of theinsulating layer.
 4. The OLED display device of claim 1, wherein thepower supply comprises: a connection metal layer on the insulating layerand contacting the center portion of the second electrode through theopening of the insulating layer; and a flexible printed circuitcontacting the connection metal layer at an edge of the substrate. 5.The OLED display device of claim 1, wherein the first electrodecomprises a transparent or transflective material, and the secondelectrode comprises a reflective material.
 6. An organic light emittingdiode (OLED) display device comprising: a substrate; a first electrodeon the substrate; an organic emission layer on the first electrode; anda second electrode on the organic emission layer, wherein a thickness ofan area of the second electrode at a center of the substrate is largerthan a thickness of an area of the second electrode at an edge of thesubstrate.
 7. The OLED display device of claim 6, wherein the firstelectrode comprises a transparent or transflective material, and thesecond electrode comprises a reflective material.
 8. The OLED displaydevice of claim 6, further comprising a power supply electricallycoupled with the second electrode at the edge of the substrate andconfigured to supply power to the second electrode.
 9. The OLED displaydevice of claim 8, wherein the power supply comprises a flexible printedcircuit.
 10. The OLED display device of claim 6, further comprising aninsulating layer substantially covering the second electrode and havingan opening exposing a center portion of the second electrode, and apower supply electrically coupled with the second electrode through theopening of the insulating layer and configured to supply power to thesecond electrode.
 11. The OLED display device of claim 10, wherein thepower supply comprises a flexible printed circuit contacting the centerportion of the second electrode through the opening of the insulatinglayer.
 12. The OLED display device of claim 10, wherein the power supplycomprises: a connection metal layer on the insulating layer andcontacting the center portion of the second electrode through theopening of the insulating layer; and a flexible printed circuitcontacting the connection metal layer at the edge of the substrate.